Johri Bhavdish N, Sharma A, Virdi J S
Department of Microbiology, G. B. Pant University of Agriculture and Technology, Pantnagar-263 145, India.
Adv Biochem Eng Biotechnol. 2003;84:49-89. doi: 10.1007/3-540-36488-9_2.
The rhizosphere or the zone of influence around roots harbors a multitude of microorganisms that are affected by both abiotic and biotic stresses. Among these are the dominant rhizobacteria that prefer living in close vicinity to the root or on its surface and play a crucial role in soil health and plant growth. Both free-living and symbiotic bacteria are involved in such specific ecological niches and help in plant matter degradation, nutrient mobilization and biocontrol of plant disease. While the rhizosphere as a domain of fierce microbial activity has been studied for over a century, the availability of modern tools in microbial ecology has now permitted the study of microbial communities associated with plant growth and development, in situ localization of important forms, as well as the monitoring of introduced bacteria as they spread in the soil and root environment. This interest is linked to environmental concerns for reduced use of chemicals for disease control as well as an appreciation for utilization of biologicals and organics in agriculture. Indian researchers have studied the diversity of rhizobacteria in a variety of plants, cereals, legumes and others along with assessment of their functionality based on the release of enzymes (soil dehydrogenase, phosphatase, nitrogenase, etc.), metabolites (siderophores, antifungals, HCN, etc.), growth promoters (IAA, ethylene) and as inducers of systemic disease resistance (ISR). Based on such primary screening protocols, effective rhizobacteria have been field tested with success stories from various agroecological zones of the country, as reflected in the control of root- and soil-borne diseases, improved soil health and increased crop yields. Several commercial formulations, mostly based on dry powder (charcoal, lignite, farmyard manure, etc.) have been prepared and field tested, however, problems of appropriate shelf-life and cell viability are still to be solved. Also, inherent in such low cost technologies are the problems of variability in field performance and successful establishment of introduced inoculants in the root zone. In addition, most products available in the market are not properly monitored for quality before they reach the farmer. As a consequence, the acceptance of rhizobacterial formulations in the country is limited. However, several laboratories have now developed protocols for the rapid characterization of effective isolates based on molecular fingerprinting and other similar tools. Also, the use of molecular markers (gus, lux, gfp, etc.) makes it easy to monitor introduced inoculants in situ in soil and rhizosphere environments. The government initiative in integrated nutrient management and pest management systems has provided additional incentives to relate rhizobacterial science to other ongoing activities so that the benefit of this research leads to technologies that are environmentally and socially acceptable.
根际或根周围的影响区域含有大量受非生物和生物胁迫影响的微生物。其中占主导地位的是根际细菌，它们更喜欢生活在根部附近或其表面，对土壤健康和植物生长起着至关重要的作用。自由生活细菌和共生细菌都参与了这些特定的生态位，并有助于植物物质降解、养分活化和植物病害的生物防治。虽然根际作为激烈微生物活动的领域已经被研究了一个多世纪，但微生物生态学中现代工具的可用性现在使得研究与植物生长和发育相关的微生物群落、重要形态的原位定位以及监测引入的细菌在土壤和根环境中的传播成为可能。这种兴趣与减少化学物质用于疾病控制的环境问题以及对农业中生物制品和有机物质利用的认识有关。印度研究人员研究了多种植物、谷物、豆类等中的根际细菌多样性，并根据酶（土壤脱氢酶、磷酸酶、固氮酶等）、代谢物（铁载体、抗真菌剂、HCN等）、生长促进剂（IAA、乙烯）以及作为系统抗病性诱导剂（ISR）的释放情况评估了它们的功能。基于这样的初步筛选方案，有效的根际细菌已经在该国不同农业生态区进行了田间试验，并取得了成功案例，体现在对根际和土传病害的控制、改善土壤健康和提高作物产量方面。已经制备并进行了田间试验的几种商业制剂，大多基于干粉（木炭、褐煤、农家肥等），然而，合适的保质期和细胞活力问题仍有待解决。此外，这种低成本技术固有的问题是田间性能的变异性以及引入的接种剂在根区的成功定殖。此外，市场上大多数产品在到达农民手中之前没有得到适当的质量监测。因此，根际细菌制剂在该国的接受度有限。然而，现在有几个实验室已经开发出基于分子指纹识别和其他类似工具对有效分离株进行快速表征的方案。此外，使用分子标记（gus、lux、gfp等）使得在土壤和根际环境中原位监测引入的接种剂变得容易。政府在综合养分管理和病虫害管理系统方面的举措提供了额外的激励措施，将根际细菌科学与其他正在进行的活动联系起来，以便这项研究的益处能够带来环境和社会可接受的技术。
